i've used this one successfully, but mix dry ingredients and wet ingredients separately before combining quickly. don't have to mix them together properly, the mixture sort of 'fizzes' when you combine

as you can see in the ingredients it has double the raising agent (SR flour plus baking powder), so much more aerated

muffins are usually made by keeping dry and wet ingredients separate until the last minute, then mixing, also often liquid fat (melted butter or oil). muffins tend to have bigger air pockets, which i think is to do with the raising agent and often added acid via buttermilk etc

cupcakes/fairy cakes i would first cream butter and sugar together before adding eggs then flour etc, the crumb is denser and more cake-like (iyswim)